The present invention relates to a resin-coated copper foil, and a printed wiring board using the resin-coated copper foil.
A resin-coated copper foil has widely been used for manufacturing printed wiring boards, because the resin layer thereof constitutes the insulating layer of a printed wiring board that contains no backbone materials, such as glass cloth represented by glass-epoxy prepreg. The resin layer of the heretofore-used resin-coated copper foil is often constituted using an epoxy-based resin composition.
The background of using such a resin composition is that the resin composition has excellent electrical properties and insulating reliability. Also, since the insulating layer of a printed wiring board contains no backbone materials, such as glass cloth, it excels in workability for forming holes when via holes are formed using laser processing, and enables the finished state of the inner walls of the via holes to be fine; therefore, it has frequently been used as a material for multi-layer printed wiring boards formed using a build-up method.
And the epoxy resin then constituting the resin layer of the resin-coated copper foil has been used after adding a flame retardant resin, such as a brominated epoxy resin and TBBA (tetrabromobisphenol A), which is a bromine-based flame retardant, so as not to ignite due to the short-circuiting of an electric circuit to cause fire, and so as to ensure anti-tracking and flame retardant ability.
Using these methods, the epoxy resin and epoxy-resin composition have been made flame retardant, and have been used as the materials constituting the resin layer of the resin-coated copper foil as materials that possess the above-described excellent electrical properties and insulating reliability, and have an excellent self-extinguishing properties.
At the same time, from recent increasing concerns on environmental problems, the elimination of halogen compounds represented by bromine from the epoxy resin has also been studied. This is because halogen compounds may form harmful compounds such as dioxins, unless properly combusted after disposal. In other words, conversion to halogen-eliminated resin compositions, known as xe2x80x9chalogen-free resinsxe2x80x9d has already been carried out in the market.
As the specific methods to form a halogen-free resin, a method in which a flame retardant inorganic filler represented by aluminum hydroxide is added to epoxy resins; a method in which a resin or the like containing red phosphorus, a phosphoric ester, or other phosphorus component is added; or a method in which a nitrogen-containing resin is used as a curing agent of the epoxy resin have been proposed.
However, although a flame-retardant epoxy resin can be manufactured without making the resin composition that constitutes the resin layer of the resin-coated copper foil contain halogens by adopting a method similar to the above-described methods, the following problems exist in each method.
For example, when flame retardation is imparted with the use of an inorganic filler, the cured resin composition tends to become hard and brittle. Therefore, if a printed wiring board is manufactured with the use of a resin-coated copper foil produced by forming a resin layer with this resin composition, the peeling strength of the cured resin layer from the copper foil is significantly lowered, and it becomes difficult to secure bond strength between the copper foil layer and the cured resin layer.
When a phosphorus compound is added, it has been pointed out that the water resistance and heat resistance of the resin are degraded, and there is a problem that the reliability of the printed wiring board lowers. In the case of the method to use a nitrogen-containing resin is used as the curing agent of the epoxy resin, since a resin composition containing a large quantity of nitrogen is used, toxic cyan compounds or Nox, which can be the subject of regulating exhaustion, may be produced when the waste is incinerated, as in the case of using halogen compounds, and improvement is demanded.
The inventors of the present invention have conceived a resin-coated copper foil and a printed wiring board that solve the above-described problems and have excellent electrical properties and insulation reliability as a material for printed wiring boards obtained as a result of repeated examinations.
According to claims, a resin-coated copper foil comprises a resin layer on one side of a copper foil, and is characterized in that the resin layer comprises a resin composition having the following composition. And the resins that constitute the resin composition comprise: a. a high polymer having cross-linkable functional groups in the molecule and a cross-linking agent thereof (5 to 30 parts by weight); b. an epoxy resin that is liquid at room temperature (5 to 30 parts by weight); and c. a compound having a structure shown in Formula 1 (40 to 90 parts by weight).
Here, since the high polymer components in the xe2x80x9chigh polymer having cross-linkable functional groups in the molecule and a cross-linking agent thereofxe2x80x9d must react with the cross-linking agent used in combination to form a three-dimensional structure, they are premised on having cross-linkable functional groups in the molecule. The cross-linkable functional groups used herein may be any one or more of alcoholic hydroxyl groups, carboxyl groups, and phenolic hydroxyl groups. Specifically, the use of any of a polyvinyl acetal resin, a phenoxy resin, carboxyl-group-modified acrylonitrile-butadiene resin, and a polyether sulfone resin is most preferable. The use of a high polymer prepared by blending two or more of these resins is also possible.
The cross-linking agents used in combination with the above-described high polymer include a urethane resin, a phenolic resin, and a melamine resin. The mixing ratio of the polymer component and the cross-linking agent is not to be specifically limited, but can be empirically determined depending on the manufacturing process and the type of the product. Therefore, the present invention was judged to require no specific limitation. Also, about the cross-linking agents used in this time, one cross-linking agent may be used alone, or two or more cross-linking agents may be used in combination at the same time.
The proportion of the above-described high polymer and cross-linking agent should be determined considering the control of resin flow and the inhibition of the generation of resin powder from the end portion of the copper clad laminate during hot pressing in the process of the copper clad laminate using the resin-coated copper foil. As a result of repeated studies by the inventors of the present invention, it was found that when the total quantity of the resin composition is 100 parts by weight, the high polymer having cross-linkable functional groups in the molecule, and a cross-linking agent thereof occupy 5 to 30 parts by weight. If the content is less than 5 parts by weight, resin flow becomes excessively large, and the generation of resin powder from the end portion of the copper clad laminate increases. On the other hand, if the content is more than 30 parts by weight, resin flow becomes small, and defects such as voids are easily produced in the insulating layer of the copper clad laminate.
Next, the xe2x80x9cepoxy resin that is liquid at room temperaturexe2x80x9d is used for securing anti-cracking properties required for the resin-coated copper foil. That is, strictly speaking, the resin-coated copper foil is a copper foil having a resin layer on one side thereof. And the resin layer is to constitute an insulating layer when a printed wiring board is manufactured using the resin-coated copper foil. Therefore, the resin layer in the state of the resin-coated copper foil is in a partly cured state, and is completely cured by hot pressing for processing to a copper clad laminate. When an epoxy resin that is liquid at room temperature is used as a constituting material for the resin composition, significant improvement of anti-cracking properties to prevent cracking that occurs on the resin layer in the partly cured state is expected.
As the specific compounds that fall in the xe2x80x9cepoxy resins that are liquid at room temperaturexe2x80x9d, the use of bisphenol-A-type, bisphenol-F-type, and bisphenol-AD-type compounds are preferable. The use of these resins is preferable, because the insulating layer obtained by processing into a copper clad laminate using a resin-coated copper foil has excellent insulation reliability, and has favorable physical properties.
The epoxy resin that is liquid at room temperature occupies 5 to 30 parts by weight when the total quantity of the resin composition is 100 parts by weight. If the content is less than 5 parts by weight, resin cracking is easily produced. On the other hand, if the content is more than 30 parts by weight, the surface of the resin becomes adhesive at room temperature, and handling becomes difficult.
The xe2x80x9ccompound having the structure shown in Formula 1xe2x80x9d is a compound having the structure shown in formula 1. 
where R is H or 
and n=1 to 10,
wherein said compound is present in the resin composition in an amount of from 40 to 90 parts by weight of the resin composition. The compound having the structure shown in Formula 1 excels in flame retardation by itself. When this resin is contained in the resin composition, practically sufficient flame retardation can be obtained without adding other special flame retardant agents. When R is H, it is a phenolic compound that acts as a curing agent for the epoxy resin. When it is used as a phenolic compound, it may be used as the curing agent of the above-described b, and when it is used in the state of an epoxy resin, an ordinary curing agent for the epoxy resin can be used. Furthermore, these phenolic compound and epoxy resin can be used in combination.
The xe2x80x9ccompound having the structure shown in Formula 1xe2x80x9doccupies 40 to 90 parts by weight when the total quantity of the resin composition is 100 parts by weight. If the content is less than 40 parts by weight, flame retardation cannot be ensured, and if the content is more than 90 parts by weight, the use of the minimum quantities necessary for exerting the effect of adding the xe2x80x9chigh polymer having cross-linkable functional groups in the molecule, and a cross-linking agent thereofxe2x80x9d and the xe2x80x9cepoxy resins that are liquid at room temperaturexe2x80x9d components, which are other components used in combination, becomes impossible.
The components other than the xe2x80x9chigh polymer having cross-linkable functional groups in the molecule, and a cross-linking agent thereofxe2x80x9d, and the xe2x80x9cepoxy resins that are liquid at room temperaturexe2x80x9d and the xe2x80x9ccompound having the structure shown in Formula 1xe2x80x9d can be used within the range not deviating from the spirit of the present invention. Specifically, these include an anti-foaming agent, a leveling agent, and a coupling agent; and the addition of these agents may contribute to the improvement of the resin-coated copper foil and the surface characteristics, and the improvement of adhesion between the copper foil and the resin layer.
The above-described resin composition is generally dissolved in a solvent such as methyl ethyl ketone, applied to the one side of a copper foil, and heated and dried to form a resin-coated copper foil. This resin-coated copper foil is used in the same manner as in ordinary copper foils to manufacture a copper clad laminate, and using this copper clad laminate, a printed wiring board can be obtained by etching and the like. For example, a resin-coated copper foil according to the present invention is laminated on a predetermined inner-layer core material, and hot-pressed, and through processes such as circuit formation and the via-hole formation by laser, a multi-layer printed wiring board is obtained. Then, in claim 4, a printed wiring board is manufactured using a resin-coated copper foil described in claims 1 to 3.